The present invention relates to improvements in the construction of bullets for smooth bore shotguns.
Various bullets or like projectiles for smooth bore shotguns have been known for some time and which are encased within a conventional casing and simply consist of bodies of lead, or similar metal, in the form of large, rough spherical elements, very heavy cylindrical bodies, which bear against the cork, base part, or filter, which seats against the explosive powder charge. This type of projectile has, in practice, been abandoned by manufacturers due to its technical shortcomings, in particular due to its excessive weight, the escape of the thrust gases involved by combustion of the powder charge, the fact that the centre of gravity in the body is not balanced, low velocity and accuracy, and for other reasons.
After the appearance of these early bullets, the German firm Brenneke developed, more than fifty years ago, an improved bullet consisting of a cylindrical lead body which had a blunt tip and whose outer surface was formed with helical ribs. The rear end of the lead body was attached to a felt plug and cardboard discs by means of a simple screw or rivet. This bullet developed by the firm Brenneke is still available and is used by the majority of loaders of cartridge bullets. Since the appearance of this Brennke-1920 bullet, other similar bullets and like projectiles have been designed, but have not afforded substantial advantages.
Another interesting and pertinent invention, made many years ago, was the bullet invented by the German firm Brennstoffwerk, of Schonebeck (Elbe). In this bullet the metal nose or head part, also based on the Brenneke-1920 bullet but with wider and deeper ribs, was attached to a plastic base part comprising a pin with disc-shaped plates serving to prevent escape of the gases. However, this assembly was heavy, and its disc-like plates were not compatible with good ballistics, as the shock of the air applied pressure and stress to its grooves. Like the Brenneke bullet, this cylindrical bullet rubbed against the walls of the gun barrel, reducing velocity and impairing the "shocks" or construction in the barrel of the gun. On the other hand, the above-mentioned German bullets have, around their blunt tip, a peripheral forward wall at their front end. In the case of some, more modern, bullets the lead part has been surrounded by a sheathing of plastic material so as not to affect adversely the gun barrel. However, the lethal efficacy is appreciably reduced due to the fact that they do not expand when hitting the target. In the case of other bullets separate (extraneous) bodies have been provided in the combined assembly of the head part (made of lead) and of the base part. Examples of these separate or extraneous parts are screw-threaded studs and nails of a harder metal, the outer surface of both of the bodies being provided with deep grooves and helical ribs, but these adversely affect the stability of the bullet in flight, render the article more expensive, and require more personnel for assembly.
Furthermore, both the Brenneke bullets and also those based on them (including the last-mentioned bullets) are subject to the drawback that the way in which the head (nose) body and the base body are joined together at the longitudinal pin--by means of a screw, rivets, screwthreaded stud, or some other separate element--results in oscillations and other disturbing movements being produced which affect the trajectory of the bullet. The better the centering, the more the difficulties increased. Independently of this, and as has already been stated, the provision of a screwthreaded stud, screw, or some similar attaching means, increases the price of the bullet, and assembly is more complicated.
It has been possible to demonstrate scientifically (making use of spark photography and supersonic tunnel tests) that the above-described types of bullet suffer from the serious defect--which is one amongst others and which cannot in any way be solved--that they do not have the correct movement of rotation when in flight, as the grooves of their outer surface do not direct the air, because they are too small in the case of some of these ribs, and due to their excessive height and increase of the angle of attack in the case of other ribs.
Also, it has been demonstrated that, when the angle of attack is increased by means of wide and deep grooves on the outer surface and also at the mouth of the gun barrel, the bullet or like projectile is rotated more quickly at supersonic speeds, whereas the bullet loses speed appreciably in the course of its flight towards the target when subsonic speeds have been reached. On the other hand, the increase in speed of rotation is not in any way equivalent to any significant improvement in the accuracy of the bullet (indeed, the contrary is the case), and this is truer still when the bullet is fired at a target lying at a distance of from 30 or 35 meters from the firearm. It is logical, as it is necessary, for obtaining a greater rotational velocity, to increase the helical angle, the depth of the grooves, and the height of the ribs, with in its turn, an increase in the angle of attack and the corresponding lateral stress or tension. To sum up, it is considered to be the case that the first-mentioned bullets suffer from the drawback of imperfect sealing, of too great a weight, of slow speed, of low stability, of low accuracy beyond a distance of a few meters, and of rendering the gun barrel unusable (smoothing out "shocks", pitting and wearing the tube). In addition the last-mentioned bullets (Brenneke-type, with small improvements in detail) entail the use of accessories which are extraneous to the body of the bullet for effecting mutual attachment of the nose part and base part of the bullet, the use of these extraneous accessories causing disturbances in the trajectory of the bullets. Also, the ribs of these bullets, whether these ribs are only small or are of pronounced size, usually do not impart correct rotational movement (doubt must be cast on the accessory nails, made of hard metal, and on the screwthreaded studs which are used, for the above-mentioned reasons and due to the fact that they are expensive, complicated, and unnecessary).
With a view to resolving the problems and shortcomings referred to above, and to obtaining advantages over the above-mentioned bullets (better range and penetration, better precision, higher speed and greater self-stabilising, greater ease in assembly, and saving in materials and labour, better sealing of the gases, and better protection of the barrel of the firearm), a composite bullet has been disclosed in a recent patent granted to the present inventor, which bullet consists of:
a metallic nose or head part, which is in the form of a single unit made by injection moulding of lead, including hardening, this nose part being of a novel shape or of a modified conventional shape. This incorporates the improvements of reduced weight, smaller diameter, a shape which is gently conical, aerodynamically satisfactory, and perfectly well stabilised, the greater weight being concentrated in the center axis of the front (impact) zone, and grooves and ribs being formed on the outer surface.
an intermediate thin disc or resilient ring made of lubricated felt, cork or fibrous material, which, in addition to serving as a damping or cushioning element, rubs against the bore of the gun barrel--due to the fact that the diameter of this disc is greater than that of the nose part of the bullet--and cleans the bore of impurities, oxides and powder residues,
a rear part, which is made of plastic material, is also gently conical, and serves as a stabilising terminal or plug part and, in its front area, has a protuberance or stud which passes through the fibrous disc, so that it is retainingly lodged in the metal nose (head) part while it has, in its rear portion, a friction band, which conincides with the diameter of the bore of the gun barrel and acts as a friction zone; its rear end is concave, so as to constitute a peripheral rim or skirt for sealing off the gases.
These main characteristics for the bullets in the above-mentioned patent of the present inventor afforded--as tests carried out have demonstrated--important advantages over the previously known bullets. The value afforded by the advantages remains unaltered at the present time.